Anyway to check for duplicate entries?

I'm wondering if its possible to check for duplicate entries in a workbook, across multiple sheets.

What I have is a list that keeps track of product in stock for clients. Every so often it happens that an entry is duplicated because the client has more than one product.

I would like to have it setup so that if a clients name is duplicated, it could merge the data into the existing row, or at least warn me of a duplicate entry.


Can it be done?